The gradation of standing timber is an important step in harvesting timber. The value of standing timber must be appraised to determine the stumpage value of a forest. Stumpage value is the value of the sale price of the standing timber. Stumpage value is determined by ascertaining the volume of the timber and the grade of the timber which is subtracted from the cost of growing, harvesting, and transporting the timber to market. The stumpage value is typically determined per thousand board feet of timber.
The harvesting of timber is generally done by clear cutting all standing trees within a given area, called a timber sale. The trees are felled, cut, bucked, and cut into logs. The log volume is determined by considering the minimum tree diameter, the top diameter, and the length in feet. The log is then given a grade based on the minimum diameter (top diameter). Log grades determine the value of each log, as logs are sold by grade. Log grades for Douglas Fir trees range from a #4 saw log, which has a minimum diameter requirement of less than 6 inches, to a #1 peeler log (suitable for peeling veneer), with a minimum diameter of 30 inches. There are three other grades for Douglas Fir trees, which are: #3 saw log, with a minimum diameter of 6 inches; #2 saw log, with a minimum diameter of 12 inches; and special mill log, with a minimum diameter of 16 inches. The value of each grade increases rapidly. Thus, there is a need for the timber cutter to quickly ascertain the proper diameter before a felled tree is cut into logs.
As stated above, during harvesting, and after a tree is felled, the timber cutter must quickly determine the diameter of the tree to see if it falls within a desired range or grade. Presently, timber cutters use a Biltmore Projection Scale which permits the direct reading of the diameter of the tree from a projection measurement. FIG. 1 shows a Biltmore scale 10 in use by a timberman 12 prior to the felling of a tree 14.
The Biltmore scale consists of a straight rule having an origin 16 at the center thereof. The timberman 12 is presumed to have a typical arm length 18 of approximately 25 inches. The scale 10 has a plurality of markings increasing in magnitude to the left and to the right of the origin 16. The timberman sights across the scale 10 to the perimeter of the tree 14 and reads the corresponding measurement on either side of the origin 16. The measurements are positioned a distance "x" from the origin such that when the origin of the scale is positioned tangent to the circumference of the tree and the distance from the eye of the observer to the origin of the scale is approximately 25 inches, the projected tree diameter can be read off either side of the scale. The projection of the tree diameter on to the scale gives a true reading of the tree diameter.
By the law of similar triangles and the Pythagorean theorem, the distance "x" from the origin at which markings corresponding to the tree diameter should be selected is defined by the following equation: ##EQU1## where a=25 inches and D equals a range of tree diameters.
Use of the Biltmore scale shown in FIG. 1 is very inconvenient for the timberman. As a result thereof, timbermen tend not to use the scale and merely judge or estimate the diameter of the tree. Consequently, inaccurate gradation of timber occurs and trees of the wrong diameter are often felled. The Biltmore scale is particularly inconvenient to use for two reasons. First, the scale itself is unwieldy because of its length of approximately 30 inches. When manufactured in a foldable form, the scale must, of course, be unfolded prior to use. A more perplexing second problem involves the cooperative use of the Biltmore scale with a chain saw prior to the felling of a tree. Gas-powered chain saws are commonly used by modern timbermen to fell large trees. Operation of the chain saw after the engine has warmed up requires continuous attention to prevent stalling. Specifically, the chain saw engine tends to stall unless the throttle is regularly operated to maintain the engine at a minimum rpm. In particular, if the chain saw is set down, such as to pick up and use a Biltmore scale, the chain saw may stall and require restarting. Hot chain saws are notoriously balky on restarting and may, in fact, not restart until the engine has cooled sufficiently.
For these reasons, the Biltmore scale is not always used by timbermen to grade trees before felling. This results in waste and inefficient cutting of timber.
Therefore, a need exists for a tree diameter projection scale which can be used without directing the timberman's attention away from operation of the chain saw at idle.